1. Field of the Invention
This invention is directed to a process for the production of N,N'-bis-(3-aminophenyl)-ureas by reacting alkyl-substituted m-phenylene diamines with urea in chlorobenzene as solvent.
2. Description of the Prior Art
It is known that diaminodiphenyl ureas can be obtained by phosgenating the corresponding nitroanilines to form the dinitrodiphenyl urea and subsequent catalytic reduction to the diamine, cf. for example the synthesis of III described by I. L. Khmel'nitskaya et al in Zh. Obsh. Khim 30 (2) (1960), page 602, or the synthesis of N,N'-bis-(5-amino-2-methylphenyl)-urea IV described by W. R. Turner and L. M. Werbel in J. Med. Chem. 28 (1985), page 1738. ##STR2##
Apart from the generally poor yields of the overall reaction, the primary disadvantage of these syntheses is the expensive reduction step.
Another two-step synthesis for the production of diaminodiphenyl ureas is the reaction of N-acetyl-p-phenylene diamine with urea and subsequent hydrolysis of the protective acetyl group which is described by H. Schiff and A. Ostrogovick in Liebigs Ann., 293. 1896, on pages 371 et seq with reference to the example of N,N'-bis-(4-aminophenyl)-urea. The disadvantage of this process is that monoacetylated diamines, which are generally not easy to prepare, have to be used as starting components.
Special p-phenylene diamines, in which the reactivity of an NH.sub.2 group is greatly reduced by suitable o-substituents, can be directly reacted with phosgene to form the corresponding aminocarbanilides. Suitable diamines include 2,5-diaminosulfonic acid (DRP 140613, Frl. 11, 1292) or 2,6-dichloro-p-phenylene diamine (DRP 268658, Frl. 11, 164). Under these conditions, other phenylene diamines result in polyureas which are totally unsuitable as reactive chain-extending agents.
A simple one-step process is the reaction of p-phenylene diamine with urea in aqueous solution as described in U.S. Pat. No. 2,503,797. Substantially pure N,N-bis-(4-aminophenyl)-urea is obtained in a high yield. However, when m-phenylene diamines are used as starting materials, the corresponding ureas--according to the teaching of the above-mentioned patent--can only be obtained in high yields substantially free from oligomers if four equivalents of sulfuric acid are added. For working up, the sulfuric acid salt of the urea which is precipitated has to be converted by reaction with BaCl2 into the corresponding chloride from which the free base can then be obtained.
Finally, U.S. Pat. No. 1,617,847 describes the production of N,N'-bis-(4-aminophenyl)-ureas by the reaction of p-phenylene diamine and alkyl-substituted p-phenylene diamines with urea in bulk or in inert solvents such as o-dichlorobenzene. However, if 2,4-diaminobenzene (TDA-2,4) is used under the conditions described in the examples of the above-mentioned patent, only an oligourea of low NH value is obtained, which is totally unsuitable for the applications envisaged.
In conclusion, it may be said that previously known processes are either too expensive, are only suitable for special diamines or only provide the desired low molecular weight ureas where p-substituted phenylene diamines are used as starting materials.
An object of the present invention is to provide a simple synthesis for ureas based on ortho-alkyl-substituted phenylene diamines.
Two aspects are of particular significance in this regard. On the one hand, the process should lead to low molecular weight ureas because, as already discussed, polyureas are unsuitable as chain-extending agents due to their inadequate reactivity. On the other hand, the proportion of monomeric starting amine in the urea products should be reduced as much as possible to eliminate
(1) any physiological risk in handling the product and PA0 (2) the adverse effect which free, aromatic low molecular weight amines are known to have on the stability of the PUR plastics produced with them to light and discoloration.
Surprisingly, this object may be achieved by the reaction of ortho-alkyl-substituted m-phenylene diamines with urea in chlorobenzene as solvent at a molar ratio of phenylene diamine to urea of greater than 2:1.